What is the smallest number of shaded squares that must be added so that the lines AB and CD are both lines of symmetry ?

(A) 2

(B) 3

(C) 4

(D) 6

What is the smallest number of shaded squares that must be added so that the lines AB and CD are both lines of symmetry ?

(A) 2

(B) 3

(C) 4

(D) 6